Hey Luis:
You basically have it
1) AudioInterval[] already dumps intervals without Table, so your construction will produce 3 sets of intervals.
2) I got it to look like you want (and produce output) by typing the command like this:
int2 = AudioIntervals[a, Slot[prop[[3]]] < 0.1 &] (* same as you had above *)
Then select the (entire) Slot[] invocation.
Use the menu item Evaluation>>Evaluate in Place. That produces this:
I have never understood how to use Front-End tokens, but you can probably use the Evaluate front-end token (i.e. ref/frontendobject/Evaluate) to automate this with Table[].
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